The human immunodeficiency viruses are among an enlarging family of human and simian retroviruses that exhibit extraordinary molecular and biological diversity. We propose to examine biological consequences of human and simian immunodeficiency virus infection of CD4+ cells in three specific areas: 1). We will continue efforts to define the interactions of HIV and SIV with the CD4 molecule and identify mechanisms through which this interaction contributes to infection and cytopathic effects. Recent studies have shown that some strains of HIV-2 as well as SIV vary in the extent to which they bind to and down modulate CD4, and that these effects may correlate with reduced cytopathicity. Using a number of isolates of HIV-1, HIV-2 and SIV, as well as laboratory-derived variants of these viruses, we will attempt to determine the mechanism for these differences. In addition we will investigate the possibility that at least some of this biological diversity arises from differences in the affinity of the viral envelope for the CD4, and determine if cellular molecules in addition to CD4 are involved. 2). We will evaluate the role of the 3'ORF viral gene product, recently termed NEF, on viral replication during HIV and SIV infection and explore potential effects of this protein on infected cells. Immunoprecipitation and Western blot assays will be utilized to quantitate NEF gene products and to identify both myristylated and phosphorylated forms of this protein in infected cells. Isolates of HIV-1 with mutations in the NEF gene, will be used to determine the effects of NEF on CD4 expression and phosphorylation as well as on a variety of signal transduction pathways in lymphoid cells. In addition, the potential for cellular pathways to regulate virus production through their effects on NEF expression or phosphorylation will also be evaluated. 3). Recent studies have indicated that HIV-1 expression may produce functional alterations in signal transduction pathways in peripheral blood lymphocytes. Using a panel of novel hybrid cell lines obtained by the fusion of antigen- responsive T cell clones and T cell leukemia lines, we will evaluate the effects of viral infection on signal transduction mechanisms through the T cell antigen receptor and other surface molecules. Biochemical alterations in phospholipid metabolism, calcium fluxes, and protein phosphorylation will be analyzed. A variety of isolates of HIV-1, HIV-2 and SIV will be evaluated including a recently described isolate of HIV-2 (HIV-2ST) from West Africa that has been shown to have reduced cytopathicity in vitro, as well as laboratory-derived biological variants of these viruses.